Computer systems that use what is known as a "graphical user interface", first introduced to the market by Apple, and later adopted by Microsoft with its "Windows" program, and by IBM with OS/2 and Presentation Manager, are a fairly recent addition to the state of the art. One common feature of these graphical user interface systems is that a multitude of windows or viewports can be present simultaneously on the computer display screen. Different application programs can be running (or waiting for input from the user) concurrently in each of the windows displayed on the computer display screen. In addition, a single application program can generate many different windows. The user can use a mouse or other input device to move back and forth between different windows, thereby performing many different tasks.
While these graphical user interface systems offer many advantages over more conventional operating systems such as DOS (which can only run and display one application program at a time), this additional function has created new problems for the user. While graphical user interface systems offer the capability of presenting a nearly unlimited number of windows on a computer screen, this does not mean that these nearly unlimited number of windows can be displayed on a computer screen so they can be seen by a user. In fact, it is quite probable that the vast majority of these windows will be either partially or completely obscured by other windows. This problem can occur with as little as two windows, but is exasperated when many more windows than this are used.
When some of the windows are partially or completely obscured, it becomes very difficult for the user to successfully move back and forth between the various windows, since the user is unable to find many of them without a significant amount of effort. This limitation in graphical user interface systems tends to defeat the very purpose of having such a system by severely restricting the number of different tasks or application programs that can really be used concurrently and displayed or otherwise presented simultaneously via windows.